G. 't Hooft discusses the concept of "naturalness" in gauge theories, emphasizing that physical parameters should be small only if their replacement would enhance the symmetry of the system. This principle is applied to construct models with complete naturalness for elementary particles, particularly focusing on the possibility that currently considered elementary fermions could be composite. Chiral symmetry is crucial for the masslessness of these fermions, and the author searches for QCD-like models where chiral symmetry is not or only partially broken spontaneously. The search is challenging due to index relations that often cannot be satisfied by unphysical fractional indices. The introduction also highlights the importance of causality and the philosophical stance that macroscopic properties should follow from microscopic equations without requiring precise matching of parameters at different energy scales. The author conjectures that this naturalness principle is why light, weakly interacting scalar particles have not been observed.G. 't Hooft discusses the concept of "naturalness" in gauge theories, emphasizing that physical parameters should be small only if their replacement would enhance the symmetry of the system. This principle is applied to construct models with complete naturalness for elementary particles, particularly focusing on the possibility that currently considered elementary fermions could be composite. Chiral symmetry is crucial for the masslessness of these fermions, and the author searches for QCD-like models where chiral symmetry is not or only partially broken spontaneously. The search is challenging due to index relations that often cannot be satisfied by unphysical fractional indices. The introduction also highlights the importance of causality and the philosophical stance that macroscopic properties should follow from microscopic equations without requiring precise matching of parameters at different energy scales. The author conjectures that this naturalness principle is why light, weakly interacting scalar particles have not been observed.